Pseudomonas aeruginosa Potentiates the Lethal Effect of Intestinal Ischemia-Reperfusion Injury: The Role of In Vivo Virulence Activation

Abstract

Introduction Experimental models of intestinal ischemia reperfusion (IR) injury are invariably performed in mice harboring their normal commensal flora, even though multiple intestinal IR events occur in humans during prolonged intensive care confinement when they are colonized by a highly pathogenic hospital flora. The aims of this study were to determine if the presence of the human pathogen P. aeruginosa in the distal intestine potentiates the lethality of mice exposed to intestinal IR and to determine what role if any in vivo virulence activation plays in the observed mortality. Methods 7-9 week old C57/BL6 mice were exposed to 15 minutes of superior mesenteric artery occlusion (SMAO) followed by direct intestinal inoculation of 1.0 × 106 CFU of P. aeruginosa PAO1 into the ileum and observed for mortality. Reiterative studies were performed in separate groups of mice to evaluate both the migration/dissemination pattern and in vivo virulence activation of intestinally inoculated strains using live photon camera imaging of both a constitutive bioluminescent P. aeruginosa PAO1 derivative XEN41 and an inducible reporter derivative of PAO1, the PAO1/lecA∷luxCDABE that conditionally expresses the quorum sensing dependent epithelial disrupting virulence protein PA-IL. Results Mice exposed to 15 minutes of SMAO and reperfusion with intestinal inoculation of P. aeruginosa had a significantly increased mortality rate (p<0.001) of 100% compared to <10% for sham operated mice intestinally inoculated with P. aeruginosa without SMAO and intestinal IR alone (<50%). Migration/dissemination patterns of P. aeruginosa in mice subjected to intestinal IR demonstrated proximal migration of distally injected strains and translocation to mesenteric lymph nodes, liver, spleen, lung, and kidney. A key role for in vivo virulence expression of the barrier disrupting adhesin PA-IL during intestinal IR was established since its expression was enhanced during IR and mutant strains lacking PA-IL displayed attenuated mortality. Conclusions The presence of intestinal P. aeruginosa potentiates the lethal effect of intestinal IR in mice in part due to in vivo virulence activation of its epithelial barrier disrupting protein PA-IL.

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